Easily the most frustrating (and heartbreaking) part of keeping pond fish is losing them to predators. Whether the fish have vanished without trace or you’ve found their remains, it helps to know what is most likely to have taken them so you can take steps to protect your remaining and future fish.
The first thing to remember is that it is not personal! Predatory birds and animals have spent many thousands of years evolving and learning to be successful hunters, and it’s only in the last few centuries that we have conveniently started keeping ornamental fish. To survive, wild animals will always take the easiest option, so your challenge is to turn your pond from an all-you-can-eat fish restaurant to an impenetrable fortress!
Where are my fish?
Like most animals, fish have a good survival instinct and will hide if they feel threatened, so it’s very likely that if some have been taken by a predator, the rest are now hiding away at the bottom of the pond. It can take several weeks for them to forget the danger and build up the confidence to swim around in the open again. Resist the urge to poke around under the plants or empty the pond to look for them—if they are hiding then they are safe, which buys you some time to predator-proof your pond. It’s also a good time to add a tonic or stress-relieving medicine to help them recover!
What took my fish?
Heron These very intelligent predatory birds are nearly 1m tall and experts at catching fish in fast-flowing rivers, streams and lakes. They have infinite patience and have perfected the art of catching fish even in murky, plant-choked water. Their long legs let them wade into deep water where they stand very still until a fish swims close enough and then they spear it with their beak. They can stand in your pond or at the side (and even on a raised edge!). They are most active at dawn and dusk, particularly through the winter when food is harder to find in the wild. They often use garden ponds to teach their young how to fish because it’s so much easier with level access and crystal clear water! They can take small and large fish. Signs that a heron has visited include an oily scum on the surface of the pond, floating feathers, fish with stab wounds (treat these with an antibacterial medicine so they don’t become infected), and the fish hiding or acting ‘jumpy’ if you go near the pond. If you’ve found dead fish with stab-wounds and loose scales scattered around the pond it’s most likely a heron that’s responsible. The only sure way to protect your fish from a heron is to cover the pond with a net.
Otter Expert fish-hunters, otters are the perfect shape for slipping under fences and netting! They hunt by diving into the pond and chasing/catching the fish underwater, so the only way to stop them is to have a strong mesh covering the whole of the pond. This will need to be securely anchored as they are strong: just pinning the corners with bricks or pegs won’t be enough. An adult otter can be over 1m long and can easily catch even the largest pond fish. They normally take the fish to the side of the pond to eat it (or carry it back home for their young). They eat most of the fish (starting with the head) but may leave the tail and big bones. Otter visits are very common now, especially if you live within 2 miles of a permanent natural water source (river, lake or reservoir).
Mink These slinky little predators are much smaller than otters (only about 30-40cm long) but hunt in a similar way and can stay underwater for several minutes at a time. The tell-tale sign that a mink is responsible for your missing fish is drag marks and lots of loose scales on the ground next to the pond where they have struggled with the weight of the fish .
Cat It’s very unlikely that your missing fish were taken by a cat: most cats show no interest in catching fish, preferring to hunt something more interesting and less wet! If they do catch fish they don’t tend to eat all of it; just cherry-pick the best bits and leave the head and tail.
Crows, magpies and other birds have been known to help themselves to fish, and if your fish are missing their dorsal fins or have wounds on their backs, birds are likely the cause. Fish are especially vulnerable in hot weather or when they are ill because they stay near the surface where there is more oxygen.
How do I protect my fish?
COVER NET and TRIP WIRE A cover net must be taut (not sagging or it can be dangerous for small birds and wildlife) and cover every part of the pond. Many people make the mistake of leaving one end clear of the net because it has good plant cover, but herons in particular are experts at fishing through dense plant cover! Trip wires (e.g. fishing line) need to be at varied heights of 30-60cm in a double ring around the perimeter of the pond to make it difficult for a heron to walk up to the edge.
ROOFING Although having a shelter or pergola over the pond won’t stop the heron accessing the pond to fish, it will stop him seeing the pond in the first place when he flies over. Water is very sparkly/reflective and herons will often spot a new pond on their way somewhere else, cruise down for a closer look and sit on a fence/rooftop/in a tree until they are sure the coast is clear before they drop down into the garden to fish. If they can’t see the pond as they are flying over they won’t even know it’s there!
DECOYS and MOTION-ACTIVATED SCARERS Sometimes plastic or resin replicas of herons or other birds can be a deterrent, but animals usually learn that they are inanimate and no threat. The best approach is to change things around regularly: keep moving the decoys and have things that flutter/rattle/sparkle. Many people have had success with wind chimes, windmills/mobiles and reflective objects (like a CD suspended on a string that will twist in the wind and catch the light). Some motion-activated scarers are available which make a noise or squirt water when triggered—these work quite well but can also upset pets and wildlife you’re trying to attract (and neighbours!).
REPELLANTS and ULTRA-SONIC EMITTERS There are several chemical animal-repellent products available to buy but be careful using these near the pond as rainfall can wash the chemicals into the pond and harm fish and wildlife. Remember that the unpleasant smells and sounds you are installing to deter predators will also drive away other animals that you might not want to discourage (like hedgehogs, songbirds or pets).
POND DESIGN and ROUTINE Making sure your pond is as large and deep as possible with plenty of surface cover and underwater hiding places will give your fish the best chance of survival. Make sure you have good filtration and aeration— fish are often targeted when they come up to the surface for air on a hot day if there isn’t enough circulation. Try to vary your routine so you are not always near the pond at the same time of day and don’t leave fish food floating on the surface—your fish are vulnerable if they come up to feed when you’re not there and excess food will even attract some predators!
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